Patent GB-813890-A (GB)
Title: A process for the preparation of aromatic carboxylic acids and their salts and other derivatives
IPC: C07C309/58
Filed: 1957-06-28
Abstract: A process for the production of an aromatic carboxylic or sulpho-carboxylic acid comprises heating at a temperature above 200 DEG  C. and in the presence of carbon dioxide, either a salt of an aromatic sulphonic acid in the presence of an acid-binding substance or a salt of an aromatic acid of phosphorus in which the phosphorus atom is bound directly to an aromatic ring, and so obtaining a salt of an aromatic carboxylicsulpho-carboxylic acid which may then be acidified to form the free acid, or converted into an other salt or into an ester or acid chloride.  The process is particularly applicable to the production of benzoic and terephthalic acids. Sulphonic acid salts which may be used are those of mono- and poly-sulphonic acids of benzene, naphthalene, biphenyl, and other aromatic compounds, including those containing alkoxy, halogen, hydrocarbon, and other nuclear substituents besides the sulphonic group, e.g. they may be salts of benzene sulphonic acid, toluene sulphonic acids, a - and b -naphthalene sulphonic acid, isomeric methylnaphthalene sulphonic acids, m-benzene-di-sulphonic acid, naphthalene disulphonic acids, and diphenylsulphonesulphonic acids. Salts of aromatic acids of phosphorus which may be used may be those of phenyl phosphonic acid, tolyl phosphonic acids, 4-ethoxy-phenylphosphonic acid, a - and b -naphthylphosphonic acids, biphenylphosphonic acids, phenylphosphonous acid, and methylphenyl-phosphonic acid.  Preferably alkali metal or alkaline-earth metal salts,s e.g. potassium salts or mixtures of potassium and sodium salts, are used.  Carbon dioxide may be present also in combined form as a carbonate in addition to the free gaseous form.  Carbonates of potassium, magnesium, calcium and aluminium may be present, or instead of the carbonates, alkali metal or alkaline-earth metal oxides, hydroxides, bicarbonates, or oxalates, may be used.  The reagents are preferably used in anhydrous condition and the reaction is preferably effected in the absence of oxygen. The reaction may be effected at temperatures between 200 DEG  and 500 DEG  C.  Yields of sulphocarboxylic acids tend to increase with lower reaction temperatures, while at higher temperatures larger amounts of carboxylic acids not containing sulphonic acid groups are obtained. The reaction may be assisted by the presence of a heavy metal or compound thereof, e.g. zinc, cadmium, lead, mercury, iron, bismuth, or thallium.  Inert fillers may also be present, e.g. carbon, kieselguhr, bentonite, metal powders or turnings, or inert salts such as sodium or potassium sulphate or phosphate.  Organic solvents such as benzene, toluene, xylene, and higher-boiling petrols, may be present.  In an example, potassium benzenesulphonate is heated in an autoclave with potassium carbonate, the double salt, potassiumcadmium chloride-fluoride, and carbon dioxide at 400 DEG  C. under a pressure rising to 170 atm., and the product is dissolved in water, the solution filtered, acidified with hydrochloric acid, and again filtered while hot to separate terephthalate acid, p-sulphobenzoic acid being isolated by extraction of the filtrate with ether.  In other examples, terephthalic acid is obtained by heating a mixture of dipotassium phenylphosphonate, potassium carbonate, cadmium fluoride, and carbon dioxide (introduced in liquid form), to 300 DEG  C. under a pressure rising to 1780 atm.; benzoic acid is obtained by heating dipotassium phenylphosphonate, potassium carbonate, cadmium fluoride, and carbon dioxide at 260 DEG  C. for 20 hours under a pressure rising to 1600 atm.